Tropical Storm TOMAS

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TROPICAL STORM TOMAS DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL212010
500 AM AST SAT OCT 30 2010
THE SATELLITE PRESENTATION OF TOMAS HAS IMPROVED OVERNIGHT. AN
EARLIER GAP IN THE DEEP CONVECTION NEAR THE CENTER HAS FILLED IN
...AND THE OUTFLOW REMAINS EXCELLENT. ALSO...IMAGERY FROM THE RADAR
ON MARTINIQUE AND A 0624 UTC TRMM PASS SUGGEST THAT AN EYEWALL
MAY BE FORMING. BASED ON THESE TRENDS...THE INITIAL INTENSITY IS
RAISED TO 60 KT. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS
SCHEDULED TO INVESTIGATE TOMAS LATER THIS MORNING TO GET BETTER
INFORMATION ON THE STRUCTURE AND INTENSITY OF THE CYCLONE. DURING
THE NEXT DAY OR SO...CONDITIONS APPEAR FAVORABLE FOR CONTINUED
INTENSIFICATION. IN FACT...THE SHIPS MODEL RAPID INTENSITY INDEX
SHOWS A NEARLY 60 PERCENT CHANCE OF A 25-KT INCREASE IN 24 HOURS.
BEYOND THAT TIME...THE SHIPS MODEL...BASED ON GFS MODEL FIELDS...
SHOWS AN INCREASE IN SOUTHWESTERLY SHEAR...WHICH SHOULD SLOW THE
RATE OF INTENSIFICATION SOMEWHAT. AFTER 72 HOURS...THE SHEAR MAY
RELAX AND ALLOW FOR FURTHER INTENSIFICATION. THE NEW OFFICIAL
FORECAST REFLECTS THIS THINKING AND IS ABOVE ALL OF THE RELIABLE
INTENSITY MODELS THROUGH THE PERIOD.
THE CENTER APPEARS TO BE LOCATED A LITTLE NORTH OF THE PREVIOUS
FORECAST TRACK BASED ON THE RECENT TRMM PASS...AND THE INITIAL
MOTION ESTIMATE IS 300/13. TOMAS IS CURRENTLY BEING STEERED
WEST-NORTHWESTWARD TO THE SOUTH OF A MID-LEVEL RIDGE THAT EXTENDS
FROM THE CENTRAL ATLANTIC INTO THE NORTHEASTERN CARIBBEAN. AS A
MID-LEVEL TROUGH CURRENTLY SITUATED OVER THE SOUTHWESTERN ATLANTIC
LIFTS OUT...ANOTHER RIDGE WILL BUILD IN NORTH OF TOMAS...WHICH
SHOULD IMPART A WEST-NORTHWESTWARD OR WESTWARD MOTION THROUGH 72
HOURS. BEYOND THAT TIME...THE GLOBAL MODELS SHOW A LONGWAVE TROUGH
MOVING INTO EASTERN NORTH AMERICA AND A CUTOFF LOW DEVELOPING IN
THE GULF OF MEXICO. THIS SHOULD WEAKEN THE RIDGE AND CAUSE A
DECREASE IN FORWARD SPEED LATE IN THE PERIOD...AND POTENTIALLY A
NORTHWARD TURN. THE TRACK MODEL ENVELOPE HAS SHIFTED NORTHWARD WITH
THIS CYCLE...BUT THE FORECAST IS ADJUSTED ONLY SLIGHTLY NORTHWARD
OUT OF RESPECT FOR THE GFS...UKMET...AND ECMWF MODELS WHICH REMAIN
FARTHER SOUTH. LATE IN THE PERIOD...THE FORWARD SPEED IS QUITE SLOW
DUE TO THE LARGE UNCERTAINTY IN THE TIMING AND SHARPNESS OF THE
POTENTIAL NORTHWARD TURN.
FORECAST POSITIONS AND MAX WINDS
INITIAL 30/0900Z 12.9N 59.5W 60 KT
12HR VT 30/1800Z 13.5N 61.3W 70 KT
24HR VT 31/0600Z 14.1N 63.7W 80 KT
36HR VT 31/1800Z 14.6N 65.9W 85 KT
48HR VT 01/0600Z 15.1N 68.1W 90 KT
72HR VT 02/0600Z 15.5N 71.5W 90 KT
96HR VT 03/0600Z 16.0N 73.5W 100 KT
120HR VT 04/0600Z 16.5N 74.5W 100 KT
$$
FORECASTER BRENNAN
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